垂直上升内螺纹管内流动沸腾传热特性

Flow boiling heat transfer characteristics in vertical upward internally ribbed tube

在压力9～22 MPa,质量流速450～2000 kg·m?2·s?1,内壁热负荷200～700 kW·m?2的参数范围内,试验研究了用于1000 MW超超临界锅炉??28.6 mm×5.8 mm垂直上升内螺纹水冷壁管内汽水流动沸腾传热。研究表明:内螺纹管内壁螺纹的漩流作用可抑制偏离核态沸腾(DNB)传热恶化,内螺纹管在高干度区发生蒸干型(DO)传热恶化。增大质量流速可推迟壁温飞升,壁温飞升幅度随质量流速增大而降低。热负荷越大管壁温越高,随热负荷增大管壁壁温飞升提前,且传热恶化后壁温飞升值增大。随着压力增加,壁温飞升发生干度值减小。内螺纹管汽水流动沸腾传热系数呈?形分布,传热系数峰值出现在汽水沸腾区。文中还给出了亚临界压力区内螺纹管单相区和汽水沸腾区的传热系数试验关联式。

In sub-critical pressure region, the heat transfer characteristics of water flowing in a vertical upward internally ribbed tube with diameter of 428.6 minx5.8 mm were experimentally investigated. The tests were performed under various conditions with pressures from 9 to 22 MPa, mass velocities from 450 to 2000 kg . m^-2 . s^-1, and inner wall heat fluxes from 200 to 700 kW . m^-2. The results show that the internally ribs of tube can effectively restrain the heat transfer from deterioration by keeping nucleate boiling. The heat transfer deterioration of dry out occurs at high steam quality in the internally ribbed tube. The increase of mass velocity can defer the sharp rise of wall temperature. The range of the sharp rise of wall temperature decreases as the mass velocity increases. With the increase of inner wall heat flux, the sharp rise of wall temperature occurs ahead at smaller steam quality, and the peak wall temperature after heat transfer deterioration increases. The steam quality corresponding to the sharp rise of wall temperature decreases at higher pressure. ＇the laeat transfer coeincaent distribution curve of internally ribbed tube is in a shape of ra The top region of heat transfer coefficient is in steam-water flow boiling region. Based on the experiments, correlations of heat transfer coefficients are presented for vertical upward internaUy ribbed tubes.